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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.math3.stat.descriptive.summary;
+
+import java.io.Serializable;
+
+import org.apache.commons.math3.exception.MathIllegalArgumentException;
+import org.apache.commons.math3.exception.NullArgumentException;
+import org.apache.commons.math3.stat.descriptive.AbstractStorelessUnivariateStatistic;
+import org.apache.commons.math3.util.MathUtils;
+
+/**
+ * Returns the sum of the squares of the available values.
+ * <p>
+ * If there are no values in the dataset, then 0 is returned.
+ * If any of the values are
+ * <code>NaN</code>, then <code>NaN</code> is returned.</p>
+ * <p>
+ * <strong>Note that this implementation is not synchronized.</strong> If
+ * multiple threads access an instance of this class concurrently, and at least
+ * one of the threads invokes the <code>increment()</code> or
+ * <code>clear()</code> method, it must be synchronized externally.</p>
+ *
+ */
+public class SumOfSquares extends AbstractStorelessUnivariateStatistic implements Serializable {
+
+ /** Serializable version identifier */
+ private static final long serialVersionUID = 1460986908574398008L;
+
+ /** */
+ private long n;
+
+ /**
+ * The currently running sumSq
+ */
+ private double value;
+
+ /**
+ * Create a SumOfSquares instance
+ */
+ public SumOfSquares() {
+ n = 0;
+ value = 0;
+ }
+
+ /**
+ * Copy constructor, creates a new {@code SumOfSquares} identical
+ * to the {@code original}
+ *
+ * @param original the {@code SumOfSquares} instance to copy
+ * @throws NullArgumentException if original is null
+ */
+ public SumOfSquares(SumOfSquares original) throws NullArgumentException {
+ copy(original, this);
+ }
+
+ /**
+ * {@inheritDoc}
+ */
+ @Override
+ public void increment(final double d) {
+ value += d * d;
+ n++;
+ }
+
+ /**
+ * {@inheritDoc}
+ */
+ @Override
+ public double getResult() {
+ return value;
+ }
+
+ /**
+ * {@inheritDoc}
+ */
+ public long getN() {
+ return n;
+ }
+
+ /**
+ * {@inheritDoc}
+ */
+ @Override
+ public void clear() {
+ value = 0;
+ n = 0;
+ }
+
+ /**
+ * Returns the sum of the squares of the entries in the specified portion of
+ * the input array, or <code>Double.NaN</code> if the designated subarray
+ * is empty.
+ * <p>
+ * Throws <code>MathIllegalArgumentException</code> if the array is null.</p>
+ *
+ * @param values the input array
+ * @param begin index of the first array element to include
+ * @param length the number of elements to include
+ * @return the sum of the squares of the values or 0 if length = 0
+ * @throws MathIllegalArgumentException if the array is null or the array index
+ * parameters are not valid
+ */
+ @Override
+ public double evaluate(final double[] values,final int begin, final int length)
+ throws MathIllegalArgumentException {
+ double sumSq = Double.NaN;
+ if (test(values, begin, length, true)) {
+ sumSq = 0.0;
+ for (int i = begin; i < begin + length; i++) {
+ sumSq += values[i] * values[i];
+ }
+ }
+ return sumSq;
+ }
+
+ /**
+ * {@inheritDoc}
+ */
+ @Override
+ public SumOfSquares copy() {
+ SumOfSquares result = new SumOfSquares();
+ // no try-catch or advertised exception here because args are valid
+ copy(this, result);
+ return result;
+ }
+
+ /**
+ * Copies source to dest.
+ * <p>Neither source nor dest can be null.</p>
+ *
+ * @param source SumOfSquares to copy
+ * @param dest SumOfSquares to copy to
+ * @throws NullArgumentException if either source or dest is null
+ */
+ public static void copy(SumOfSquares source, SumOfSquares dest)
+ throws NullArgumentException {
+ MathUtils.checkNotNull(source);
+ MathUtils.checkNotNull(dest);
+ dest.setData(source.getDataRef());
+ dest.n = source.n;
+ dest.value = source.value;
+ }
+
+}